Method for producing renewable fuel

ABSTRACT

A process for preparing hydrocarbons from an oxygenated hydrocarbon feedstock, such as animal fat, having a high nitrogen impurity is described. Hydrotreatment of the oxygenated feedstock occurs in a first hydrotreating bed arranged downstream of a polishing bed. A gaseous phase is removed and the liquid hydrotreated phase is fed to the polishing bed arranged upstream of the first hydrotreating bed together with fresh hydrogen. The process effectively removes nitrogen impurities from the resultant hydrocarbon product causing an improved cloud point after isomerisation, and the arrangement makes efficient use of fresh hydrogen for polishing, providing a polished hydrocarbon product rich in dissolved hydrogen. Part of the product can be used as hydrocarbon diluent in the downstream hydrotreating bed, and/or withdrawn between the polishing and hydrotreating bed and isomerised in an isomerisation reactor.

TECHNICAL FIELD

The present invention relates to processes for preparing hydrocarbonsfrom an oxygenated hydrocarbon feedstock having nitrogen impurities, andin particular to an efficient utilisation of hydrogen in such processes.

BACKGROUND ART

Converting fossil oils (such as crude oils) and renewable oils (such asplant oils or animal fats) into valuable products, such astransportation fuels (e.g. gasoline, aviation fuel and diesel) involvehydrotreating processes, which consumes hydrogen.

Refining of heavy crude oil and low quality plant oils and animal fats,such as waste animal, fat increases the hydrogen demand in hydrotreatingprocesses. Thus, generating, recovering and purchasing of hydrogen forhydrotreatment of oil have significant impact on refinery operatingcosts.

Hydrotreating of fossil and renewable oils are performed with an excessof hydrogen compared to the theoretical consumption. The hydrogenremaining after hydrotreating step may be purified and recycled togetherwith additional fresh hydrogen to make up for the hydrogen consumed inthe hydrotreating step, the so-called make-up hydrogen.

During hydrotreating a number of reactions occur to various extentsdepending on the feedstock composition. Hydrotreating reactions includedouble bond hydrogenation, hydrodeoxygenation (HDO),hydrodesulfurisation (HDS), hydrodenitrification (HDN),hydrodearomatisation (HDAr), hydrocracking (HC) and hydroisomerisation.

Hydroisomerisation is typically done on a bifunctional catalyst havingboth metal dehydrogenation function and acidic function, for exampleplatinum or palladium catalysts together with molecular sieves such asSAPO-11. Isomerisation selectivity of the catalyst is important, i.e.typically hydrocracking that also occurs to a certain extent duringhydroisomerisation is suppressed, if during hydrotreatment it is notdesired to reduce the average molecular weight of feed. This involves abalance between metal dehydrogenation function and acidic functions,which is sensitive to elements that can shift this balance. It isspeculated that amines neutralise strong acid sites, leading to lowcatalyst acidity and activity. Sulfur is known to poison the metaldehydrogenation function of noble metal catalysts.

One of the common feed impurities include nitrogen, which are well-knownconstituents of oil of fossil and of renewable origin, as well as animalwaste fat. In crude oil average nitrogen impurity contents of 940 w-ppmand contents as high as 7500 w-ppm has been reported (Manrique et al.(1997) Basic Nitrogen Compounds in Crude Oils: Effect on MineralDissolution During Acid Stimulation Processes, SPE-37224-MS;https://www.onepetro.org/conference-paper/SPE-37224-MS). It is also notuncommon that animal waste fat can contain 1000 ppm nitrogen or evenhigher. The typical way of handling undesirable impurities infeedstocks, such as nitrogen impurities, is to purify the feedstockprior to hydrotreatment. It is typical to remove the water-solublenitrogen compounds through degumming. However, in animal fat, a majorpart of the nitrogen compounds are oil soluble, and much more difficultto remove than the water-soluble nitrogen compounds.

US 2011/0094149 A1 (to IFP Energies Nouvelles) describes methods ofhydrotreating feeds from renewable sources in two catalytic zones usinga molybdenum catalyst, where the gaseous and liquid effluent from thebeds having a higher temperature at the outlet than at the inlet, due tothe exothermic nature of the hydrotreatment reaction, is used directlyas recycle to heat fresh feed to the catalytic zones. US 2011/0094149 A1exemplifies the invention using good quality palm oil and soy oil havinga small nitrogen impurity of 15 and 23 ppm, respectively, and mentionsthat feeds from renewable sources generally contain various impurities,such as a nitrogen impurity of generally 1-100 ppm, and even up to 1 wt%.

US 2011/0094149 A1 reduces the nitrogen amount in the examples to about2% of the original amount and does not hydrotreat any impure feed havinga nitrogen content outside the general range of 1-100 ppm. Comparativeexample 1 hydrotreats and isomerises animal fat having a nitrogencontent of about 1 wt % at process conditions described in US2011/0094149 A1, showing that it is possible to hydrotreat impure feedshaving a nitrogen content outside the general range of 1-100 ppm.However, the nitrogen content after the hydrodeoxygenation stages isabout 2-5 ppm, and after isomerisation, the yield of aviation fuel cutwas only 5% having a high pour point of −10° C. compared to therequirements for aviation fuels.

Consequently, there is a need for further hydrotreatment processes thatcan effectively hydrotreat oxygenated hydrocarbons having a nitrogenimpurity outside the general range of 1-100 ppm and ensure a lownitrogen amount in the hydrotreated product. Additionally, there is aneed for processes that can produce a high quality aviation fuel cuthaving good cold flow properties from oxygenated hydrocarbons having anitrogen impurity outside the general range of 1-100 ppm.

There is a possibility of purifying the feed further beforehydrogenation to remove as much nitrogen as possible. However, whilepurification methods to remove water soluble nitrogen are easilyimplemented, a lot of the nitrogen content in animal fat is oil soluble,and much more difficult to remove.

Additionally, there is a need for more efficient use of hydrogen, whichis added in excess and usually recycled.

SUMMARY OF THE INVENTION

The present invention was made in view of the prior art described above,and the object of the present invention is to provide

a process that can improve the quality of a hydrotreated productobtained from an oxygenated hydrocarbon feed containing nitrogenimpurities, while at the same time making more efficient use of thehydrogen. In particular the improved quality at least includes a lowamount of nitrogen impurity in the product, as well as improved coldflow properties of the isomerised product.

To solve the problem, the present invention provides a process forpreparing hydrocarbons from an oxygenated hydrocarbon feedstock having anitrogen impurity of 10 wppm or more, measured as elemental nitrogen,where the process comprises a reactor (101) comprising a first catalyticzone/polishing zone (102) arranged upstream of a second catalyticzone/hydrotreatment zone (105). The oxygenated hydrocarbon feedstock isfed to the hydrotreatment zone and the effluent from the firsthydrotreating zone is purified, and where the purified effluent from thefirst hydrotreating zone (108) is hydrotreated at a higher temperaturein the polishing zone (102) and where the feed to the polishing zone(102) is not mixed with an oxygenated hydrocarbon feedstock, i.e. is notmixed with fresh feed.

Specifically, the invention relates to a process for preparinghydrocarbons from an oxygenated hydrocarbon feedstock having a nitrogenimpurity of 10 wppm or more, measured as elemental nitrogen, comprising:

-   -   a hydrotreatment reactor (101) comprising a first catalytic zone        (102) arranged above a second catalytic zone (105), in which a        hydrotreatment entry stream comprising the oxygenated        hydrocarbon feedstock (104), a hydrogen-rich gas (120), and        optionally a product recycle diluting agent (108, 126), is        introduced to the second catalytic zone (105) at an inlet        between the first (102) and the second catalytic zone (105),        where it is mixed with part of a first hydrotreated effluent        from the first catalytic zone, where the second catalytic zone        is operated at a temperature and a pressure causing at least        hydrodeoxygenation and hydrodenitrification to an extent where a        second hydrotreated effluent (106) from the second catalytic        zone (105) of the hydrotreatment reactor contains mainly        hydrocarbons, and wherein the oxygenated hydrocarbon feedstock        has been converted to ≥95% hydrocarbons;    -   the second hydrotreated effluent from the second catalytic zone        of the hydrotreatment reactor is subjected to a separation stage        (107) where at least part of the second hydrotreated effluent        (106) is separated into a gaseous fraction (121) and a        hydrotreated liquid (108), where the hydrotreated liquid        contains ≥95 wt % hydrocarbons and >1 wppm nitrogen;    -   at least part of the hydrotreated liquid (108) and a        hydrogen-rich gas (120) is introduced into the hydrotreatment        reactor (101) to the first catalytic zone (102), at an inlet        temperature that is higher than the inlet temperature in the        second catalyst zone of the hydrotreatment reactor and at a        pressure causing hydrodeoxygenation and hydrodenitrification;    -   a product side stream (112) containing part of the first        hydrotreated effluent from the first catalytic zone (102) is        taken out between the first and second catalytic zones, the        product side stream (112) containing a liquid component and a        gaseous component, and where the liquid component of the side        stream contains ≥99 wt % hydrocarbons and ≤1 wppm nitrogen,        preferably ≤0.4 wppm nitrogen, such as ≤0.3 wppm nitrogen (the        ASTM D4629 detection), measured as elemental nitrogen;

That is, the inventors of the present invention in a first aspect of theinvention found that oxygenated hydrocarbons containing a nitrogenimpurity amount can be effectively hydrotreated in two catalytic zoneswithin a reactor, when ammonia and other low boiling amines are removedfrom the effluent from the second catalytic zone (105) (hydrotreatingzone) by separation into a gaseous and a liquid phase, followed byhydrotreating the liquid phase therefrom in a first catalytic zone (102)(polishing zone), in which this liquid phase is neither combined withother oxygenated hydrocarbon feeds, nor combined with other feeds havinga higher nitrogen content than the first hydrotreated liquid. At leastpart of the first hydrotreated effluent is taken out as a side streamand separated into a gaseous stream and a second hydrotreated liquidstream, which separation may be a stripping step or be followed by astripping step (114), where the first hydrotreated liquid stream may bestripped with a stripping gas, such as hydrogen to lower the nitrogencontent of the stripped side stream (115) to 0.3 wppm or lower.

Specifically, the inventors have found that ammonia present in thehydrogen-rich effluent gas, which has been formed from the nitrogenimpurities of the feed during hydrotreating, can be reincorporated intothe product during deeper hydrodeoxygenation/hydrodenitrificationconditions, if hydrogen-rich gas containing such ammonia impurities isused in a polishing step without prior removal of the ammonia impurity.

By using a polishing zone (first catalytic zone) upstream of ahydrotreating zone (second catalytic zone) fresh hydrogen can be betterutilised compared to a reactor with a polishing zone downstream of ahydrotreating zone. This is because the feed to the first catalytic zone(102) (polishing zone) already contains lower amounts of nitrogencompared to the oxygenated hydrocarbon feed to the second catalytic zone(105) (hydrotreating zone), and the fresh hydrogen added to thepolishing zone will not contain the nitrogen impurities that are presentin the effluent from the second catalytic zone, and at the same time,the excess hydrogen present in the effluent from the first catalyticzone (102) (polishing zone) remains of a suitable quality for use in thesecond catalytic zone (105) (hydrotreating zone).

The reactor setup and process of the present invention causes a moreefficient hydrogen usage while at the same time ensuring low amounts ofnitrogen impurities of the product product side stream (112).

The product product side stream (112) may be used as a product of itsown or it may also be isomerised in an isomerisation reactor (103)comprising at least one catalytic zone, in which the product productside stream (112) and a hydrogen-rich gas (120), which hydrogen-rich gasmay contain ≤1 ppm (mol/mol) nitrogen, measured as elemental nitrogen,is introduced into the catalytic zone at an inlet temperature and apressure causing at least hydroisomerisation to produce an isomerisedeffluent (116);

-   -   the isomerised effluent from the isomerisation reactor is        subjected to a separation stage (117), where the isomerised        effluent (116) is separated into a gaseous fraction (118) and an        isomerised liquid (119), where the isomerised liquid contains        ≥30 wt % branched hydrocarbons, and/or an increase in branched        hydrocarbons of ≥30 wt % compared to the product product side        stream (112).

For example, the side stream may be subjected to a stripping stage(114), where the side stream (116) is stripped with a stripping gas (H₂)causing the stripped side stream (115) to have ≤0.4 wppm nitrogen, suchas ≤0.3 wppm nitrogen (the ASTM D4629 detection), measured as elementalnitrogen, and a lower nitrogen amount compared to the side stream (116);may be subjected to a step of isomerising this stripped side stream(115) in an isomerisation reactor (103) comprising at least onecatalytic zone, in which the stripped side stream (115) and ahydrogen-rich gas (120) having ≤1 ppm (mol/mol) nitrogen, measured aselemental nitrogen, is introduced into the catalytic zone at atemperature and a pressure causing at least hydroisomerisation toproduce a first isomerisation effluent (116);

where the isomerised effluent from the isomerisation reactor (103) issubjected to a separation stage, where the isomerised effluent isseparated into a gaseous fraction and an isomerised liquid, where thefirst isomerised liquid contains ≥30 wt % branched hydrocarbons, and/oran increase in branched hydrocarbons of ≥30 wt % compared to thestripped side stream (115).

The isomerised liquid may be separated into at least an aviation fuelhaving a freeze point of −40° C. or lower, such as −47° C. or lower.

Cooling may be applied during the separation stage of the secondhydrotreated effluent (106) to an extent that the second hydrotreatedliquid (108) has a temperature below the inlet temperature of the firstcatalytic zone (102) of the first hydrotreatment reactor (101).

A hydrocarbon diluting agent as well as a fresh oxygenated hydrocarbonfeedstock is not intended to be introduced to the first catalytic zoneof the hydrotreatment reactor (102).

The extent of hydrodeoxygenation and hydrodenitrification in the secondcatalytic zone (105) may controlled in such a manner that in the firstcatalytic zone (102), the temperature increase between the inlet of thefirst catalytic zone and the outlet of the first catalytic zone is notmore than 10° C.

The second catalytic zone (105) in the hydrotreatment reactor (101) mayhave a lower hydrodeoxygenation activity than the first catalytic zone(102) in the hydrotreatment reactor (101).

The hydrogen-rich gas (120) used in the first catalyst zone (102) maycontain ≤5 wppm nitrogen impurities, measured as elemental nitrogen.

The inlet temperature and pressure of the second catalyst zone (105) maybe 200-400° C. and 10-150 bar, such as 250-380° C. and 20-120 bar, suchas 280-360° C. and 30-100 bar.

The second catalytic zone of the hydrotreatment reactor may comprise oneor more catalyst(s) selected from hydrogenation metal on a support, suchas for example a catalyst selected from a group consisting of Pd, Pt,Ni, Co, Mo, Ru, Rh, W or any combination of these, preferably the secondcatalytic zone comprise one or more catalyst(s) selected from CoMo,NiMo, NiW, CoNiMo on a support, for example an alumina support.

The hydrotreatment reactor (101) may be operated at a WHSV in the rangefrom 0.5-3 h⁻¹; and a H₂ flow of 350-900 NI H₂/I feed.

The inlet temperature and pressure of the first catalyst zone (102) maybe 250-450° C. and 10-150 bar, such as 300-430° C. and 20-120 bar, suchas 330-410° C. and 30-100 bar.

The first catalytic zone of the hydrotreatment reactor comprises one ormore catalyst(s), which may be selected from hydrogenation metalcompound on a support, such as for example a catalyst selected from agroup consisting of Pd, Pt, Ni, Co, Mo, Ru, Rh, W or any combination ofthese, preferably the first catalytic zone comprise one or morecatalyst(s) selected from CoMo, NiMo, NiW, CoNiMo on a support, forexample an alumina support.

The inlet temperature and pressure of the isomerisation reactor (103)may be 280-370° C. and 20-50 bar.

The catalytic zone of the isomerisation reactor comprise one or morecatalyst(s), which may comprise a Group VIII metal on a support, wherethe support is selected from silica, alumina, clays, titanium oxide,boron oxide, zirconia, which can be used alone or as a mixture,preferably silica and/or alumina.

The catalytic zone of the isomerisation reactor may further comprise amolecular sieve, such as a zeolite.

The isomerisation reactor (103) may be operated at a WHSV in the rangefrom 0.5-1 h⁻¹; and a H₂ flow of 300-500 NI H₂/I feed.

The isomerised liquid may have an i- to n-paraffin ratio above 1, suchas from 5 to or from 15 to 30.

Part of the first hydrotreated effluent from the first catalytic zone(102) may be used to heat the hydrotreatment entry stream, e.g. bymixing.

The oxygenated hydrocarbon feedstock may have a nitrogen impurity 300wppm or more, preferably 500 wppm or more, measured as elementalnitrogen.

The hydrotreatment entry stream may have a nitrogen impurity of 100 to500 wppm.

The second hydrotreated effluent (106) from the second catalytic zonemay have a nitrogen impurity of 100 to 500 wppm or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a process scheme with a hydrotreating reactor (101)comprising a first catalytic zone (102) (polishing bed) arranged above asecond catalytic zone (105) (hydrotreatment bed), and a firstisomerisation reactor (103).

FIG. 2 shows a comparative process scheme not according to the presentinvention having a first hydrotreating reactor (201) and a firstisomerisation reactor (203).

FIG. 3 shows a comparative process scheme not according to the presentinvention having a first hydrotreating reactor (301), a secondhydrotreating reactor (302) and a first isomerisation reactor (303).

DETAILED DESCRIPTION OF THE INVENTION

In describing the embodiments of the invention specific terminology willbe resorted to for the sake of clarity. However, the invention is notintended to be limited to the specific terms so selected, and it isunderstood that each specific term includes all technical equivalentswhich operate in a similar manner to accomplish a similar purpose.

The present invention relates to a process for preparing hydrocarbonsfrom an oxygenated hydrocarbon feedstock having a nitrogen impurity of10 wppm or more, measured as elemental nitrogen, comprising:

-   -   a hydrotreatment reactor (101) comprising a first catalytic zone        (102) arranged above a second catalytic zone (105), in which a        hydrotreatment entry stream comprising the oxygenated        hydrocarbon feedstock (104), a hydrogen-rich gas (120), and        optionally a product recycle diluting agent (108, 126), is        introduced to the second catalytic zone (105) at an inlet        between the first (102) and the second catalytic zone (105),        where it is mixed with part of a first hydrotreated effluent        from the first catalytic zone, where the second catalytic zone        is operated at a temperature and a pressure causing at least        hydrodeoxygenation and hydrodenitrification to an extent where a        second hydrotreated effluent (106) from the second catalytic        zone (105) of the hydrotreatment reactor contains mainly        hydrocarbons, and wherein the oxygenated hydrocarbon feedstock        has been converted to ≥95% hydrocarbons;    -   the second hydrotreated effluent from the second catalytic zone        of the hydrotreatment reactor is subjected to a separation stage        (107) where at least part of the second hydrotreated effluent        (106) is separated into a gaseous fraction (121) and a        hydrotreated liquid (108), where the hydrotreated liquid        contains ≥95 wt % hydrocarbons and ≥1 wppm nitrogen;    -   at least part of the hydrotreated liquid (108) and a        hydrogen-rich gas (120) is introduced in the hydrotreatment        reactor (101) to the first catalytic zone (102), at an inlet        temperature that is higher than the inlet temperature in the        second catalyst zone of the hydrotreatment reactor and at a        pressure causing hydrodeoxygenation and hydrodenitrification;    -   a product product side stream (112) containing part of the first        hydrotreated effluent from the first catalytic zone (102) is        taken out between the first and second catalytic zones, the        product product side stream (112) containing a liquid component        and a gaseous component, and where the liquid component of the        side stream contains ≥99 wt % hydrocarbons and ≤1 wppm nitrogen,        preferably ≤0.4 wppm nitrogen, such as ≤0.3 wppm nitrogen (the        ASTM D4629 detection), measured as elemental nitrogen.

That is, the inventors of the present invention in a first aspect of theinvention found that oxygenated hydrocarbons containing a nitrogenimpurity amount can be effectively hydrotreated in two catalytic zoneswithin a reactor, when ammonia and other low boiling amines are removedfrom the effluent from the second catalytic zone (105) (hydrotreatingzone) by separation into a gaseous and a liquid phase, followed byhydrotreating the liquid phase therefrom in a first catalytic zone (102)(polishing zone), in which this liquid phase is neither combined withother oxygenated hydrocarbon feeds, nor combined with other feeds havinga higher nitrogen content than the first hydrotreated liquid. At leastpart of the first hydrotreated effluent is taken out as a productproduct side stream (112) and separated into a gaseous stream and asecond hydrotreated liquid stream, which separation may be a strippingstep or be followed by a stripping step (114), where the firsthydrotreated liquid stream may be stripped with a stripping gas, such ashydrogen to lower the nitrogen content of the stripped side stream (115)to 0.4 wppm or lower, such as ≤0.3 wppm nitrogen (the ASTM D4629detection).

Specifically, the inventors have found that gaseous ammonia present inthe hydrogen-rich effluent gas, which has been formed from the nitrogenimpurities of the feed during hydrotreating, can be reincorporated intothe product during deeper hydrodeoxygenation/hydrodenitrificationconditions, if hydrogen-rich gas containing such ammonia impurities isused in a polishing step without prior removal of the ammonia impurity.

By using a polishing zone (first catalytic zone) upstream of ahydrotreating zone (second catalytic zone) fresh hydrogen can be betterutilised compared to a reactor with a polishing zone downstream of ahydrotreating zone. This is because the feed to the first catalytic zone(102) (polishing zone) already contains lower amounts of nitrogencompared to the oxygenated hydrocarbon feed to the second catalytic zone(105) (hydrotreating zone), and the fresh hydrogen added to thepolishing zone will not contain the nitrogen impurities that are presentin the effluent from the second catalytic zone, and at the same time,the excess hydrogen present in the effluent from the first catalyticzone (102) (polishing zone) remains of a suitable quality for use in thesecond catalytic zone (105) (hydrotreating zone).

The reactor setup and process of the present invention causes a moreefficient hydrogen usage while at the same time ensuring low amounts ofnitrogen impurities of the product side stream (112).

The process is for preparing hydrocarbons from an oxygenated hydrocarbonfeedstock. Examples of oxygenated hydrocarbon feedstocks are fatty acidsand triglycerides, which are present in large amounts in plant oils andanimal fats. An oxygenated hydrocarbon feedstock of renewable origin,such as plant oils and animal fats are well suited for the process. Themajority of these plant oils and animal fats are composed of 25 wt % or40 wt % or more of fatty acids, either as free fatty acids or as estersof free fatty acids. Examples of esters of free fatty acids are fattyacid glyceride esters (mono-, di- and/or tri-glyceridic) or for examplethe fatty acid methyl esters (FAME) or fatty acid ethyl esters (FAEE).Accordingly, the oxygenated hydrocarbon feedstocks of renewable originmay contain 40 wt % or more of fatty acids or fatty acid esters.

The renewable character of carbon-containing compositions, such asfeedstocks and products, can be determined by comparing the ¹⁴C-isotopecontent of the feedstock to the ¹⁴C-isotope content in the air in 1950.The ¹⁴C-isotope content can be used as evidence of the renewable originof the feedstock or product. Carbon atoms of renewable material comprisea higher number of unstable radiocarbon (¹⁴C) atoms compared to carbonatoms of fossil origin. Therefore, it is possible to distinguish betweencarbon compounds derived from biological sources, and carbon compoundsderived from fossil sources by analysing the ratio of ¹²C and ¹⁴Cisotopes. Thus, a particular ratio of said isotopes can be used toidentify renewable carbon compounds and differentiate those fromnon-renewable i.e. fossil carbon compounds. The isotope ratio does notchange in the course of chemical reactions. Examples of a suitablemethod for analysing the content of carbon from biological sources isASTM D6866 (2020). An example of how to apply ASTM D6866 to determinethe renewable content in fuels is provided in the article of Dijs etal., Radiocarbon, 48(3), 2006, pp 315-323. For the purpose of thepresent invention, a carbon-containing material, such as a feedstock orproduct is considered to be of renewable origin if it contains 90% ormore modern carbon, such as 100% modern carbon, as measured using ASTMD6866.

A number of plant oils and animal fats may contain typical amounts ofnitrogen impurity, such as between 1-100 ppm, which can be hydrotreatedusing the process of the present invention. However, the process of thepresent invention is advantageous from the point of view that thehydrotreatment process can convert oxygenated hydrocarbon feedstockshaving a high nitrogen impurity, for example having a nitrogen impurityof 10 wppm or more. For example 300 wppm to 2500 wppm, or more, such as500 wppm or more, for example 800 wppm or more. Oxygenated hydrocarbonfeedstocks may for example have a nitrogen impurity of up to 1500 wppm,such as up to 2500 wppm. Examples of oxygenated hydrocarbon feedstockswith high nitrogen impurity are some animal fats, which can havenitrogen impurities of about 1000 wppm, for example in the range of 600to 1400 wppm. The oxygenated hydrocarbon feedstock may be made up of amixture of oxygenated hydrocarbons from different sources, should thatbe desired. For example, 50% of a palm oil having 23 ppm nitrogenimpurity may be mixed with 50% animal fat having 1000 ppm nitrogenimpurity to create an oxygenated hydrocarbon feedstock having a nitrogenimpurity of 512 ppm. The oxygenated hydrocarbon feedstock may thereforebe selected from plant oils, animal fats, or mixtures thereof.

The nitrogen impurity is measured as elemental nitrogen. One such methodto measure elemental nitrogen is ASTM D4629, which is used in the rangeof 0.3-100 wppm, and another method is ASTM D572, which may be moreappropriate above 100 wppm. Both methods can be used as necessary in thepresent invention to measure the nitrogen impurity is as elementalnitrogen.

A hydrotreatment reactor (101) comprising a first catalytic zone (102)arranged above a second catalytic zone (105) is used in the process, andthe process involves flowing a hydrotreatment entry stream to a secondcatalytic zone (105) at an inlet between the first (102) and the secondcatalytic zone (105). The hydrotreatment entry stream comprises theoxygenated hydrocarbon feedstock (104), which can be selected asdescribed above, e.g. plant oils, animal fat or mixtures thereofcontaining 10 wppm nitrogen or more, such as 300 wppm nitrogen or more,for example between 500-1500 wppm nitrogen.

The oxygenated hydrocarbon feedstock is mixed with part of a firsthydrotreated effluent from the first catalytic zone, and optionally aproduct recycle diluting agent (108, 126). Using part of the firsthydrotreated effluent from the first catalytic zone as a hydrocarbondiluting agent is advantageous from the point of view that it containshydrocarbons with dissolved hydrogen, which results in a more effectivehydrodeoxygenation (HDO) and hydrodenitrification (HDN) in the secondcatalytic zone. Using product recycle (108, 126) as a hydrocarbondiluting agent is advantageous compared to using the first hydrotreatedeffluent as a hydrocarbon diluting agent in that a greater volume of thefirst hydrotreated effluent product can be withdrawn as a product sidestream (112).

Hydrocarbon diluting agents are well-known in the art, and are used tocontrol the exothermic character of the hydrotreating reactions (e.g.HDO and HDN reactions). Additionally, hydrocarbon diluting agents canalso contain dissolved hydrogen, which is required for efficienthydrotreatment, as the catalyst must both be in contact with theoxygenated hydrocarbon feedstock as well as hydrogen in order for thehydrotreating reactions to proceed.

Using part of the first hydrotreated effluent from the first catalyticzone (FIG. 1 , I) as a hydrocarbon diluting agent is advantageousbecause it will already contain dissolved hydrogen, and it has a hightemperature which can be used to heat the inlet of the second catalyticzone (105).

Using as the hydrocarbon diluting agent, a mixture of both the firsthydrotreated effluent from the first catalytic zone (FIG. 1 , I) andproduct recycle from the second catalytic zone (108, 126), e.g. at least10% of both, is advantageous from the point of view that fractionscontaining dissolved hydrogen is mixed with a product recycle from anearlier stage thereby increasing the amount of product side stream (112)that can be withdrawn, thereby increasing the throughput of the reactorcompared to only using the first hydrotreated effluent (FIG. 1 , I) asthe hydrocarbon diluting agent.

Part of the first hydrotreated effluent from the first catalytic zone(102) may also be used to heat the hydrotreatment entry stream, e.g. bymixing.

As mentioned, the hydrocarbon diluting agent may be product recycle(108, 126) or a hydrocarbon of either fossil or renewable origin. Itwill usually be product recycle and/or the first hydrotreated effluentfrom the first catalytic zone. A hydrocarbon diluting agent is typicallyadded in amounts ranging from 1:1 to 4:1 (total hydrocarbon dilutingagent:total oxygenated feedstock). As mentioned, the hydrocarbondiluting agent may be of fossil or renewable origin. Some hydrocarbonfeeds of fossil origin can contain a high amount of nitrogen impurities.These hydrocarbon feeds of fossil origin may also be part of thehydrocarbon diluting agent, alone or in admixture with other hydrocarbondiluting agent(s), such as product recycle and/or the first hydrotreatedeffluent from the first catalytic zone. For example the hydrocarbondiluting agent may be a mixture of product recycle and fossilhydrocarbons.

The product recycle and the first hydrotreated effluent from the firstcatalytic zone are advantageous to use as they will typically containdissolved hydrogen, which is relevant for the hydrotreatment reactionthat depends on hydrogen being dissolved in the liquid phase.

The hydrotreatment entry stream may have a nitrogen impurity of 100 wppmor more, e.g. from 100 to 500 wppm, and/or the second hydrotreatedeffluent (106) from the second catalytic zone may have a nitrogenimpurity of 100 wppm or more, e.g. from 100 to 500 wppm or more. Theprocess of the present invention is advantageous from the point of viewthat the hydrotreatment process can convert oxygenated hydrocarbonfeedstocks having a high nitrogen impurity without the need forextensive dilution to reduce the overall nitrogen impurity of thehydrotreatment entry stream. This is advantageous, as an extensivedilution would decrease the throughput of oxygenated hydrocarbonfeedstock in the hydrotreating process. Alternatively, or additionally,the nitrogen content may also be measured in the second hydrotreatedeffluent (106) from the second catalytic zone, which may have a nitrogenimpurity of 100 wppm or more, e.g. from 100 to 500 wppm or more.

As to the maximum amount of nitrogen impurity that may be present. Therewill be limitations as to how much nitrogen impurity that is present asimpurities or how high an impurity amount it is practically feasible toremove. Accordingly, the hydrotreatment entry stream and/or the secondhydrotreated effluent (106) from the second catalytic zone may have anitrogen impurity of up to 500 wppm or less, i.e. the hydrotreatmententry stream and/or the second hydrotreated effluent (106) from thefirst hydrotreatment reactor may have a nitrogen impurity of between 100and 500 wppm.

The hydrotreatment entry stream is introduced together with ahydrogen-rich gas (120) to a hydrotreatment reactor (101) comprising afirst catalytic zone (102) arranged above a second catalytic zone (105).

The hydrogen-rich gas (120) is necessary to perform i.a. thehydrodeoxygenation (HDO) and hydrodenitrification (HDN) reactions in thefirst and second catalytic zones (102, 105) of the hydrotreatmentreactor (101). The hydrogen-rich gas may for example be excess hydrogenfrom the process (123, 118) that has been purified by one or morepurification steps (122), such as for example separation (122) into agaseous fraction (123) comprising hydrogen, water, ammonia and otherlights followed by amine scrubbing and/or membrane separation. Thepurity of the hydrogen-rich gas used in the second catalytic zone is notas important as the purity of the hydrogen-rich gas used for the firstcatalytic zone (102), used for stripping before the isomerisationreactor (114) or used in the isomerisation reactor (103), which suitablydoes not contain any reactive nitrogen, such as ammonia, such as lessthan 0.3 w-ppm nitrogen, measured as elemental nitrogen. Typically, itis acceptable that the hydrogen-rich gas used for the second catalyticzone has a purity of 95 mol % or higher, but it is also possible that ithas a hydrogen purity that is lower than 95 mol %. Make-up hydrogen canalso be mixed to form the hydrogen-rich gas, or the hydrogen-rich gascan be entirely made up of make-up gas.

The hydrotreatment reactor (101) is a vessel that can house the at leasttwo catalytic zones (102, 105). In the present invention a trickle-bedreactor is well-suited. A trickle bed reactor involves the downwardmovement of the hydrotreatment entry stream while it is contacted withhydrogen in a co-current or counter-current manner. An example of atrickle bed reactor is an adiabatic trickle-bed reactor.

The hydrotreatment reactor (101) comprises a first catalytic zone (102)arranged above a second catalytic zone (105). A catalytic zone may inits simplest form be a fixed bed of catalyst particles. A catalytic zonemay contain a single fixed bed or may contain multiple fixed beds havingthe same or different catalyst particles, or it may be a number oflayers of catalyst particles of different activity and/or composition.

The first catalytic zone (102) may be a single fixed bed, and/or thesecond catalytic zone (105) may comprise at least three fixed beds.

The hydrotreatment entry stream is introduced together with ahydrogen-rich gas (120) to the second catalytic zone (105) at an inletbetween the first (102) and the second catalytic zone (105)

The hydrotreatment entry stream is introduced together with ahydrogen-rich gas (120) into the second catalytic zone at an inlettemperature and a pressure causing at least hydrodeoxygenation andhydrodenitrification to an extent where a second hydrotreated effluent(106) from the second catalytic zone (105) of the hydrotreatment reactorcontains mainly hydrocarbons.

There are many different combinations of inlet temperatures andpressures, which would cause HDO and HDN to an extent that oxygen isremoved from the oxygenated hydrocarbons thereby producing water as aby-product, and that the nitrogen impurities are removed from theoxygenated hydrocarbons thereby producing ammonia as a by-product,thereby obtaining a product containing mainly hydrocarbons.

For example, the inlet temperature and pressure of the second catalystzone (105) may be 200-400° C. and 10-150 bar, such as 250-380° C. and20-120 bar, such as 280-360° C. and 30-100 bar.

It is a matter of routine work for the skilled person to select variouscombinations of temperatures and pressures causing at leasthydrodeoxygenation and hydrodenitrification to an extent where thesecond hydrotreated effluent (106) from the second catalytic zonecontains mainly hydrocarbons, wherein the oxygenated hydrocarbonfeedstock has been converted to ≥95% hydrocarbons, suitably ≥98%hydrocarbons, where ≤2% of the oxygenated hydrocarbon feedstock ispresent.

In the same manner that the skilled person can select variouscombinations of temperatures and pressures, he would also be able toselect one or more suitable catalysts for the catalytic zone of thesecond catalytic zone (105).

For example, the second catalytic zone of the hydrotreatment reactor maycomprise one or more catalyst(s) selected from hydrogenation metal on asupport, such as for example a catalyst selected from a group consistingof Pd, Pt, Ni, Co, Mo, Ru, Rh, W or any combination of these, preferablythe second catalytic zone comprise one or more catalyst(s) selected fromCoMo, NiMo, NiW, CoNiMo on a support, for example an alumina support.

The hydrotreatment reactor (101) may be operated at a WHSV in the rangefrom 0.5-3 h⁻¹; and a H₂ flow of 350-900 NI H₂/I feed.

More general reaction conditions for the second catalytic zone (105) mayinvolve a trickle-bed reactor as the hydrotreating reactor (101),comprising the second catalytic zone, the catalytic zone comprising asupported hydrogenation catalyst comprising molybdenum, where thehydrotreatment is conducted in the presence of hydrogen at a temperatureof 200-400° C. and at a pressure between 10-150 bar, where the WHSV isin the range from 0.5-3 h⁻¹, and at a H₂ flow of 300-2100 NI H₂/I feed.

The second catalytic zone will generate a second hydrotreated effluent(106), which will contain gaseous components in the form of excesshydrogen, water vapour produced from HDO, CO and CO₂ produced fromdecarboxylation/decarbonylation of carboxylic acids in the oxygenatedhydrocarbon feed as well as H₂S. Finally, NH₃ will be produced from theHDN reaction. Much more ammonia (NH₃) will be produced in the processwhere oxygenated hydrocarbon feedstock comprising nitrogen impurities of300 wppm or more, than during hydrotreatment of normal feeds e.g. havingthe typical amounts of 1-100 ppm nitrogen, such as palm oil, which, forexample, may have 23 ppm nitrogen. The inventors surprisingly found thatespecially the increased amount of ammonia in the hydrotreatmenteffluent from oxygenated hydrocarbon feedstock comprising nitrogenimpurities of 300 wppm or more caused reincorporation of nitrogen, whenthe hydrotreated effluent was subjected to a further hydrotreatment stepwith added make-up hydrogen. That is, the inventors saw that a furtherhydrotreatment effluent from an additional hydrotreatment step contained2-5 ppm nitrogen even after stripping with hydrogen gas, i.e. even ifthere was a desire to remove nitrogen as completely as possible beforecontacting with an isomerisation catalyst, it was simply not possible toget the nitrogen amount below 2-5 ppm, even after stripping. This wasquite unexpected, as the additional hydrotreatment step was conducted athigher temperatures with the specific expectation of preforming a deeperHDO and HDN hydrotreatment, thereby removing more extensively oxygen andnitrogen from the second hydrotreatment effluent. Further, it wasexpected that the already formed hydrocarbons should be inert to anyreaction with ammonia, and even if ammonia should react to generateamines or amides under the conditions of the additional hydrotreatmentstep, that even if there was a theoretical possibility that suchnitrogen compounds would form, that these formed compounds would againundergo hydrodenitrification (HDN) removing therefrom ammonia. However,it was surprisingly found that nitrogen compounds were generated thatdid not disappear again under the hydrotreatment conditions in anadditional hydrotreatment step. Those compounds included secondary andtertiary amides.

As it is known in the art, nitrogen may deactivate the isomerisationcatalyst, which is why ammonia contained in an effluent going to anisomerisation reactor is typically stripped with a stripping gas,causing any dissolved ammonia to be displaced/stripped by the strippinggas thereby removing any remaining amounts of nitrogen. As was found bythe inventors in comparative examples 1 and 2, the absence of aseparation step between the first and second hydrotreating step(corresponding to the second catalytic zone and first catalytic zone,respectively), when hydrotreating oxygenated hydrocarbon feedstocks,will cause a higher nitrogen content to be present to be fed to theisomerisation reactor, which in turn causes a lower yield of aviationfuel cut having a cloud point of −40° C. or lower.

It was an unexpected discovery that ammonia in the first hydrotreatedeffluent of FIGS. 2 and 3 caused reincorporation of nitrogen in thesecond hydrotreatment reactor, and that these nitrogen compounds werealso unexpectedly resilient to the HDN conditions, which caused thenormal removal of any residual ammonia in the stripping step prior toisomerisation to be ineffective. This was surprising to the inventors,who modified the hydrotreatment steps by including a separation stageafter the first hydrotreatment reactor, in such a way that the secondhydrotreated effluent from the second catalytic zone of thehydrotreatment reactor is subjected to a separation stage (107) where atleast part of the second hydrotreated effluent (106) is separated into agaseous fraction (121) and a hydrotreated liquid (108).

The separation stage (107) may be for example one or more high-pressureor low-pressure separators, that are known in the art to be able toseparate the second hydrotreated effluent (106) into a gaseous fraction(121) and a second hydrotreated liquid (108). Hydrogen stripping mayalso be used for the separation (not shown in the figure). Theseparation stage may entirely be a high temperature separation stage,where the effluent is not actively cooled. Not cooling the firsthydrotreatment effluent is beneficial from the point of view that lessheating is required in the first catalytic zone. It may also bebeneficial, if the separated second hydrotreated liquid is used as aproduct recycle to dilute the oxygenated hydrocarbon feedstock.

The separation stage may also involve a low temperature separation,where the hydrotreated effluent is actively cooled by e.g. a heatexchanger, as this is beneficial from the point of view that as muchammonia as possible is separated from the first hydrotreated liquid.Accordingly, cooling may be applied during the separation stage of thesecond hydrotreated effluent (106) to an extent that the secondhydrotreated liquid (108) has a temperature below the inlet temperatureof the first catalytic zone (102) of the hydrotreatment reactor (101),such as at least 100° C. below the inlet temperature of the firsthydrotreatment reactor. Cold separation of the first hydrotreatmenteffluent may for example be performed at temperatures between 120 and200° C.

The entire amount of the second hydrotreated effluent (106) may beseparated, or at least part of the second hydrotreated effluent (106)may be separated. For example, the second hydrotreated effluent may besplit into two streams, where one stream is separated into a secondhydrotreated liquid (108) and a gaseous fraction (121) as describedabove, and where the other stream is used as a hydrocarbon dilutingagent without any separation. The other stream would in addition tohydrocarbons also include both the excess hydrogen as well as all thegaseous impurities, including ammonia, which would be reintroduced intothe second catalytic zone.

The entire amount of the second hydrotreated effluent (106) may also beseparated to avoid ammonia build-up in the second catalyst zone or toavoid adding further amounts of ammonia to the second catalyst zone(when the second hydrotreating effluent is used as product recycle),which could react with the oxygenated hydrocarbons to form furthernitrogen compounds, which could then be present in the secondhydrotreating effluent.

In the separation stage (107), the second hydrotreated effluent (106) isseparated into a gaseous fraction (121) and a second hydrotreated liquid(108). The gaseous fraction (121) will comprise excess hydrogen, watervapour produced from HDO, CO and CO₂ produced fromdecarboxylation/decarbonylation of carboxylic acids in the oxygenatedhydrocarbon feed as well as H₂S. Finally, NH₃ will be produced from theHDN reaction. The second hydrotreated liquid (108) will contain ≥90 wt %hydrocarbons, the remainder being heteroatom-containing hydrocarbons,such as unreacted oxygenated hydrocarbons. It is desirable that thehydrotreatment is as complete as possible, i.e. that the secondhydrotreated liquid (108) contains ≥95 wt % hydrocarbons, such as ≥98 wt% hydrocarbons. However, it is not always feasible or possible tocompletely hydrotreat the hydrotreatment entry stream without increasingthe severity of the reaction conditions, which could cause coking of thecatalyst, and other undesirable side effects. Accordingly, theconversion may be such that the second hydrotreated liquid (108) alsocontains ≤99 wt % hydrocarbons, i.e. the hydrotreatment entry stream ishydrotreated to an extent that the second hydrotreated liquid (108)contains between 95 and 99 wt % hydrocarbons.

The remaining components of the first hydrotreated liquid would beheteroatom-containing hydrocarbons, such as oxygenated hydrocarbons ornitrogen containing hydrocarbons. When the initial nitrogen impurity isvery high, the nitrogen will still remain to some extent in the firsthydrotreated liquid, which may contain >1 wppm nitrogen, measured aselemental nitrogen, such as >5 wppm, and up to 100 wppm.

The second hydrotreated liquid (108) containing nitrogen impurities ofe.g. 5-100 wppm, or at least part of the second hydrotreated liquid(108) is introduced in the first catalytic zone (102) together with ahydrogen-rich gas (120).

The hydrogen-rich gas (120) is necessary to perform i.a. thehydrodeoxygenation (HDO) and hydrodenitrification (HDN) reactions notonly in the second catalytic zone (105) as explained above, but also inthe first catalytic zone (102). The hydrogen-rich gas may for example beexcess hydrogen from the process (123, 118) that has been purified byone or more purification steps (122), such as for example separation(122) into a gaseous fraction (123) comprising water, ammonia and otherlights followed by amine scrubbing and/or membrane separation. Thepurity of the hydrogen-rich gas used in the second catalytic zone is notas important as the purity of the hydrogen-rich gas used for the firstcatalytic zone (102), used for stripping before the isomerisationreactor (114) or used in the isomerisation reactor (103).

The hydrogen-rich gas used for the first catalytic zone typically has apurity of 90 mol %, often 95 mol % or higher, and may contain gaseoushydrocarbons. As it is intended to reduce as much as possible the riskof reincorporating nitrogen into the first hydrotreatment effluent,withdrawn as a product side stream (112), the hydrogen-rich gas used forthe first catalytic zone (102) ideally has very little or no reactivenitrogen, such as ammonia. Specifically, the nitrogen content in thehydrogen-rich gas (120) used for the first catalytic zone (102) reactorshould ideally not cause an increase in the nitrogen content of theliquid phase of the feed (127+102) for the first catalytic zone (102)when it is mixed with the first hydrotreated liquid (127) to form thefeed (127+102) to first catalytic zone (102).

The hydrogen-rich gas (120) used in the first catalyst zone (102) maytherefore contain ≤10 wppm nitrogen impurities or lower, such as ≤5 wppmnitrogen impurities, measured as elemental nitrogen, such as ≤1 wppmnitrogen impurities, measured as elemental nitrogen.

The hydrogen-rich gas may be the excess hydrogen gas that has beenpurified, the so-called hydrogen recycle, if that has a sufficientquality. The hydrogen-rich gas may also be fresh hydrogen, which has notyet been used in the process, and it may be a mixture of the hydrogenrecycle and fresh hydrogen.

As will be appreciated by the skilled person, when reference is made tonitrogen impurities, it is intended to cover nitrogen impurities, whichunder the hydrotreating or hydroisomerisation conditions can beconsidered to react to form new bonds, i.e. non-inert or reactivenitrogen. For example, nitrogen that is capable of being incorporatedinto the products and intermediates of the present invention, such asthe second hydrotreated effluent (106), the first hydrotreatmenteffluent, withdrawn as a product side stream (112), or the isomerisationeffluent (116) is considered to be nitrogen impurities according to thepresent invention. It is not intended that nitrogen gas (N2) should fallwithin the term nitrogen impurities, as it is used in the presentinvention. Nitrogen impurities can be determined using elementalanalysis and cover organic nitrogen, ammonia, and ammonium.

As referred to above, the hydrotreatment reactor (101) comprises a firstcatalytic zone (102) arranged above a second catalytic zone (105). Thefirst catalytic zone (102) may be a single fixed bed.

At least part of the second hydrotreated liquid (108, 127) is introducedtogether with a hydrogen-rich gas (120) to a first catalytic zone (102),at an inlet temperature and a pressure causing at leasthydrodeoxygenation and hydrodenitrification, to an extent where theliquid component of the side stream contains ≥99 wt % hydrocarbons and≤1 wppm nitrogen, preferably ≤0.4 wppm nitrogen, such as ≤0.3 wppmnitrogen (the ASTM D4629 detection), measured as elemental nitrogen.

Specifically, the nitrogen content of the liquid component of theproduct side stream (112) is lower than the nitrogen content of thesecond hydrotreated liquid (108).

It is not required nor intended that the second hydrotreated liquidshould be diluted with any diluting agent, such as hydrocarbons, beforeor during hydrotreatment in the first catalytic zone (102). Rather thesecond hydrotreated liquid (108, 127) is used as the feed to the secondhydrotreating reactor. However, it is possible to mix the secondhydrotreated liquid (108, 127) with another hydrocarbon feed, as long asthe second hydrotreated liquid (108, 127) is not mixed with a feedhaving an oxygen content that is higher than the oxygen content of thesecond hydrotreated liquid (108, 127), and where the second hydrotreatedliquid (108, 127) is preferably not mixed with a feed having a nitrogencontent of ≥100 wppm;

A hydrocarbon diluting agent is not necessary to control the exothermiccharacter of the hydrotreatment reactions in the first catalytic zone.Accordingly, a diluting agent, such as a hydrocarbon diluting agent maytherefore be absent in the second hydrotreatment reactor, i.e. ahydrocarbon diluting agent is in some cases not introduced to the firstcatalytic zone of the hydrotreatment reactor (102).

There are many different combinations of inlet temperatures andpressures, which would cause HDO and HDN to an extent that oxygen isremoved from the remaining oxygenated hydrocarbons thereby producingwater as a by-product, and that the nitrogen impurities are furtherreduced compared to the second hydrotreated liquid (108) therebyproducing ammonia as a byproduct, and a liquid component of the productside stream (112) containing a lower amount of nitrogen impurities thanthe second hydrotreated liquid (108).

Specifically, the inlet temperature in the first catalyst zone (102) ishigher than the inlet temperature in the second catalyst zone (105) ofthe hydrotreatment reactor (101).

For example, the inlet temperature and pressure of the first catalyticzone (102) may be 250-450° C. and 10-150 bar, such as 300-430° C. and20-120 bar, such as 330-410° C. and 30-100 bar.

In order to cause a deeper HDO and HDN reaction, the inlet temperatureof the first catalytic zone (102) is higher than compared to the inlettemperature of the second catalytic zone (105). For example, the inlettemperature of the first catalytic zone (102) may be 10-15° C. higherthan the inlet temperature for the second catalytic zone (105), or evenhigher.

As the amount of oxygenated hydrocarbons are significantly less in thesecond hydrotreated liquid (108, 127) compared to the hydrotreatmententry stream to the second catalytic zone (105), this means that thetemperature rise over the first catalytic zone (102) is not as high asin the second catalytic zone (105) due to the fact that less exothermicreactions occurs.

For example, the temperature increase between the reactor inlet and thereactor outlet of the second hydrotreatment reactor may be small, suchas no more than 35° C., or it can be considered as being 50% or less ofthe temperature rise in the first hydrotreatment reactor.

Accordingly, the extent of hydrodeoxygenation and hydrodenitrificationin the second catalytic zone (105) may controlled in such a manner thatin the first catalytic zone (102), the temperature increase between theinlet of the first catalytic zone and the outlet of the first catalyticzone is not more than 10° C. This can be controlled by ensuring asufficient conversion of the oxygenated hydrocarbon feed in the firsthydrotreatment reactor, leaving only a small amount of hydrocarbonshaving heteroatoms such as oxygen and nitrogen in the first hydrotreatedliquid, which will then result in a smaller temperature rise due to theamount of material remaining that undergoes the exothermichydrotreatment reactions.

The second catalytic zone (105) in the hydrotreatment reactor (101) mayhave a lower hydrodeoxygenation activity than the first catalytic zone(102) in the hydrotreatment reactor (101).

To increase the hydrotreating activity in the first catalytic zone, itis possible to increase the temperature, as mentioned above, in order toobtain more extensive HDO and HDN reactions. It is also possible toincrease the hydrotreating activity by ensuring that the first catalyticzone (102) has a higher hydrodeoxygenation activity than the secondcatalytic zone (105).

The catalytic activity may also start out by being the same in both thefirst and second catalytic zones, e.g. by using a catalyst having thesame activity in both reactors. Over time the second catalytic zone(105) will deactivate faster than the first catalytic zone (102) becausea more impure feed, the hydrotreatment entry stream, is provided to thesecond catalyst zone, whereas a more pure feed, the second hydrotreatedliquid (108, 127), is provided to the first catalytic zone (102).Accordingly, the second catalytic zone (105) may have a lowerhydrodeoxygenation activity than the first catalytic zone (102).Catalytic activity can be measured compared to the fresh catalyst.

In the same manner that the skilled person can select variouscombinations of temperatures and pressures in the second catalytic zone,he would also be able to select one or more suitable catalysts andconditions to cause more extensive HDO and HDN reactions in the firstcatalytic zone.

The first catalytic zone of the hydrotreatment reactor comprise one ormore catalyst(s), which may be selected from hydrogenation metal on asupport, such as for example a catalyst selected from a group consistingof Pd, Pt, Ni, Co, Mo, Ru, Rh, W or any combination of these. Forexample, the catalytic zones may comprise one or more catalyst(s)selected from CoMo, NiMo, NiW, CoNiMo on a support, for example analumina support. When the catalyst is selected from the group consistingof Ni, Co, Mo, Ru, Rh, W or any combination of these, then typically thecatalyst is sulfided, and a source of sulfur is either added or presentin the hydrotreatment entry stream and/or in the hydrogen-rich gas.

The first catalytic zone of the hydrotreatment reactor may be operatedat a WHSV in the range from 0.5-3 h⁻¹, such as 0.5-1.5 h⁻¹ and a H₂ flowof 350-2100 NI H₂/I feed, such as 500-1500 NI H₂/I feed.

More general reaction conditions for the first catalytic zone mayinvolve a trickle-bed reactor comprising the first and second catalyticzone, the catalytic zone comprising a supported hydrogenation catalystcomprising molybdenum, where the hydrotreatment is conducted in thepresence of hydrogen at a temperature of 250-400° C. and at a pressurebetween 10-150 bar, where the WHSV is in the range from 0.5-3 h⁻¹, andat a H₂ flow of 500-2100 NI H₂/I feed.

A product product side stream (112) containing part of the firsthydrotreated effluent from the first catalytic zone (102) is taken outbetween the first and second catalytic zones. The first hydrotreatedeffluent may e.g. be collected in a tray having one or more overflowweirs or chimneys to allow effluent gas (FIG. 1 , g) to pass downstreamto the second catalytic zone (105), and to allow overflow (FIG. 1 , I)of the first hydrotreated effluent to pass downstream to the secondcatalytic zone.

A product product side stream (112) containing a liquid component andoptionally a gaseous component can be withdrawn between the firstcatalytic zone and the second catalytic zone. The liquid component ofthe side stream contains ≥99 wt % hydrocarbons and ≤1 wppm nitrogen,preferably ≤0.4 wppm nitrogen, such as ≤0.3 wppm nitrogen (the ASTMD4629 detection), measured as elemental nitrogen.

The product side stream (112) may for example be subject to one or morehigh-pressure or low-pressure separators, that are known in the art tobe able to separate the product side stream (112) into a liquid fractionand a gaseous fraction. The separation stage may entirely be a hightemperature separation stage, where the product side stream (112) is notactively cooled. Not cooling the product side stream (112) is beneficialfrom the point of view that less heating is required in any followingsteps, such as an isomerisation step.

The separation stage (114) may be a stripper, which uses a gas, usuallyhydrogen, to remove impurities in the product side stream (112) or theliquid component of the product side stream (112). Hydrogen is usuallyused as a stripping gas, because the stripping stage then both servesthe purpose of removing impurities as well as ensuring that a certainamount of hydrogen is dissolved in the liquid component of the sidestream (112) and/or the stripped liquid side stream (115), which isbeneficial if these liquids are taken to e.g. a hydroisomerisationstage, such as the isomerisation reactor (103). The nitrogen content ofthe liquid component of the product side stream (112) as well as thestripped liquid side stream (115), if stripping is used, is lower thanthe nitrogen content of the second hydrotreated liquid (108).

Accordingly, the product side stream (112) from the first catalytic zone(102) may be stripped with a stripping gas (e.g. hydrogen) subjected toa stripping stage (114) causing the stripped liquid side stream (115) tohave ≤0.4 wppm nitrogen, such as ≤0.3 wppm nitrogen (the ASTM D4629detection limit), measured as elemental nitrogen.

A stripping stage using hydrogen is beneficial to use in order to bothremove impurities as well as ensuring that a certain amount of hydrogenis dissolved in the liquid phase, as explained above. A stripping stageis in particular useful, when liquids are taken to e.g. ahydroisomerisation stage, such as the isomerisation reactor (103).

The product side stream (112) may be used as a product of its own, or itmay be further refined by isomerised.

The product side stream (112) may be isomerised in an isomerisationreactor (103) comprising at least one catalytic zone, in which theproduct side stream (112) and a hydrogen-rich gas (120), whichhydrogen-rich gas may contain ≤1 ppm (mol/mol) nitrogen, measured aselemental nitrogen, is introduced into the catalytic zone at an inlettemperature and a pressure causing at least hydroisomerisation toproduce an isomerised effluent (116).

A hydrogen-rich gas (120) is also necessary to perform thehydrodeoxygenation (HDO) and hydrodenitrification (HDN) in the first andsecond catalyst zones (102, 105) as explained above, but also in theisomerisation reactor (103).

The hydrogen-rich gas may for example be excess hydrogen from theprocess (123, 118) that has been purified by one or more purificationsteps (122), such as for example separation (122) into a gaseousfraction (123) comprising water, ammonia and other lights followed byamine scrubbing and/or membrane separation. The purity of thehydrogen-rich gas used in the isomerisation reactor is important.

The hydrogen-rich gas used for the isomerisation reactor has a purity of95% or higher. As it is intended to reduce as much as possible the riskof poisoning the catalytic zone(s) of the isomerisation reactor.Accordingly, the hydrogen-rich gas used for the second hydrotreatingreactor ideally has very little or no reactive nitrogen, such asammonia.

The hydrogen-rich gas (120) used in the isomerisation reactor (103) maytherefore contain ≤1 ppm (mol/mol) nitrogen impurities, measured aselemental nitrogen. The hydrogen-rich gas may be the excess hydrogen gasthat has been purified, the so-called hydrogen recycle, if that has asufficient quality. The hydrogen-rich gas may also be fresh hydrogen,which has not yet been used in the process, and it may be a mixture ofthe hydrogen recycle and fresh hydrogen.

As will be appreciated by the skilled person, when reference is made tonitrogen impurities, it is intended to cover nitrogen impurities, whichunder the hydrotreating or hydroisomerisation conditions can beconsidered to react to form new bonds, i.e. non-inert or reactivenitrogen. For example nitrogen that is capable of being incorporatedinto the products and intermediates of the present invention, such asthe first or second hydrotreating effluent, or the first isomerisationeffluent is considered to be nitrogen impurities according to thepresent invention. It is not intended that nitrogen gas (N2) should fallwithin the term nitrogen impurities, as it is used in the presentinvention. The sulfur impurity, if any, should also be low, when theisomerisation catalyst comprises a noble metal catalyst, such as acatalyst containing Pd or Pt.

The isomerisation reactor (103) is a vessel that can house the at leastone catalytic zone. In the present invention a trickle-bed reactor iswell-suited. A trickle bed reactor involves the downward movement of thefeed while it is contacted with hydrogen in a co-current orcounter-current manner. An example of a trickle bed reactor is anadiabatic trickle-bed reactor.

The isomerisation reactor (103) comprises at least one catalytic zone.Such a catalytic zone may in its simplest form be a fixed bed ofcatalyst particles. It may also be multiple fixed beds having the sameor different catalyst particles, or it may be a number of layers ofcatalyst particles of different activity and/or composition. Theisomerisation reactor (103) may have a single catalytic zone.

The liquid component of the side stream (112) or the stripped sidestream (115) is introduced together with a hydrogen-rich gas (120) to anisomerisation reactor (103) where it comes into contact with at leastone catalytic zone, at an inlet temperature and a pressure causing atleast hydroisomerisation to produce an isomerisation effluent (116), toan extent where the liquid part (119) of the isomerised effluent (116)contains ≥30 wt % branched hydrocarbons, and/or an increase in branchedhydrocarbons of ≥30 wt % compared to the second hydrotreated liquid.

There are many different combinations of inlet temperatures andpressures, which would cause hydroisomerisation to an extent theisomerised effluent (116) contains ≥30 wt % branched hydrocarbons,and/or an increase in branched hydrocarbons of ≥30 wt % compared to thesecond hydrotreated liquid.

For example, the inlet temperature and pressure of the isomerisationreactor (103) may be 250-400° C. and 20-50 bar, such as 280-370° C. and20-50 bar or 295-370° C. and 20-50 bar.

The catalytic zones of the first isomerisation reactor may comprise oneor more catalyst(s) comprising a Group VIII metal on a support, wherethe support may be selected from silica, alumina, clays, titanium oxide,boron oxide, zirconia, which can be used alone or as a mixture. Forexample, the support may be silica and/or alumina. The Group VIII metalmay for example be Pd or Pt. Additionally, the one or more catalyst(s)may further comprise a molecular sieve, such as a zeolite.

The isomerisation reactor (103) may be operated at a WHSV in the rangefrom 0.5-3 h⁻¹; and a H₂ flow of 150-800 NI H₂/I feed, for example 0.5-1h⁻¹; and a H₂ flow of 300-500 NI H₂/I feed.

The skilled person knows how to manipulate the above conditions in orderto obtain an extent of hydroisomerisation where the liquid part (119) ofthe first isomerisation effluent (116), contains more branchedhydrocarbons compared to the liquid component of the product side stream(112). For example to such an extent that the liquid part (119) of thefirst isomerisation effluent (116), contains ≥30 wt % branchedhydrocarbons, and/or an increase in branched hydrocarbons of ≥30 wt %compared to the second hydrotreated liquid.

The first isomerised liquid may also have been isomerised to such anextent that the iso- to n-paraffin ratio is above 1, such as from 5 to30, or from 15-30.

The degree of isomerisation is often measured as the difference betweencloud point of the feed and the product, here between the liquidcomponent of the product side stream (112) and the liquid part (119) ofthe isomerisation effluent, where a magnitude of the decrease in cloudpoint determines how extensive the hydroisomerisation has been.Accordingly, the first isomerised liquid may be isomerised to such anextent that the decrease in cloud point from the second hydrotreatedliquid and to the liquid part (119) of the first isomerisation effluentis 10° C. or more.

Normally it is considered that the lower the cloud point, the better,because this would convey good cold flow properties. However, duringhydroisomerisation conditions there is also hydrocracking to someextent. In the art there is usually a point where hydrocracking becomestoo extensive that the loss of liquid product outweighs the potentialfor a lower cloud point. The catalyst and any impurities containedtherein, as well as the conditions for hydroisomerisation are among theparameters that can influence the degree of hydroisomerisation andhydrocracking. Reference is made to the comparative example 1 andexample 1, where it can be seen that the nitrogen impurity beforeentering the isomerization reactor is much higher in the comparativeexample 1 (0.6-2.9 wppm) compared to example 1 (≤0.3 wppm). Such adifference in nitrogen content to the isomerisation reactor influencesnot only the yield of the specific fuel cut, but also significantlyinfluences the cold flow properties thereof.

For example, the side stream may be subjected to a stripping stage(114), where the side stream (116) is stripped with a stripping gas (H₂)causing the stripped side stream (115) to have ≤0.4 wppm nitrogen, suchas ≤0.3 wppm nitrogen (the ASTM D4629 detection), measured as elementalnitrogen, and a lower nitrogen amount compared to the side stream (116);may be subjected to a step of isomerising this stripped side stream(115) in an isomerisation reactor (103) comprising at least onecatalytic zone, in which the stripped side stream (115) and ahydrogen-rich gas (120) having, such as ≤0.3 wppm nitrogen (the ASTMD4629 detection), measured as elemental nitrogen, is introduced into thecatalytic zone at a temperature and a pressure causing at leasthydroisomerisation to produce a first isomerisation effluent (116);

where the isomerised effluent from the isomerisation reactor (103) issubjected to a separation stage, where the isomerised effluent isseparated into a gaseous fraction and an isomerised liquid, where thefirst isomerised liquid contains ≥30 wt % branched hydrocarbons, and/oran increase in branched hydrocarbons of ≥30 wt % compared to thestripped side stream (115).

More general reaction conditions for the isomerisation step may involvea trickle-bed reactor as the isomerising reactor, comprising a catalystzone, the catalyst zone comprising a supported hydrogenation catalystcomprising W or Pt or Pd, and a zeolite where the hydroisomerisation isconducted in the presence of hydrogen at a temperature of 295-370° C.and at a pressure between 20-50 bar, where the WHSV is in the range from0.5-1.5 h⁻¹, and at a H₂ flow of 150-800 NI H₂/I feed to such an extentthat the decrease in cloud point from the second hydrotreated liquid andto the liquid part (119) of the first isomerisation effluent is reducedby 10° C. or more.

The isomerised effluent (116) from the isomerisation reactor (103) issubjected to a separation stage (117), where the isomerised effluent(116) is separated into a gaseous fraction (118) and an isomerisedliquid (119).

The separation stage (117) may be for example one or more high-pressureor low-pressure separators, that are known in the art to be able toseparate the isomerised effluent (116) into a gaseous fraction (118) anda first isomerised liquid (119). The separation stage (117) may also bedistillation, although usually it is beneficial to separate the gaseousfraction from the liquid fraction before distillation.

As mentioned above, the first isomerised liquid contains ≥30 wt %branched hydrocarbons, and/or an increase in branched hydrocarbons of≥30 wt % compared to the second hydrotreated liquid.

The isomerised effluent (116) or the isomerised liquid (119) may besubjected to a distillation stage to produce one or more productfractions. Such fractional distillation is well-known in the art.

In particular, the process of the present invention is beneficialbecause it was surprisingly found that the specific conditions resultedin a large fraction of high quality aviation fuel, see example 1. Theaviation fuel fraction contained the C8-C16 hydrocarbons, in particularthe major part of the aviation fuel contained the C9-C12 hydrocarbons.The aviation fuel fraction may also be characterised by the distillationrange, for example as having a distillation range between 150-250° C.

The isomerised liquid may be separated into at least an aviation fuelhaving a cloud point of −25° C. or lower, such as −30° C. or lower, forexample −40° C. or lower, such as −47° C. or lower.

FIG. 1 describes feeding oxygenated hydrocarbon feedstock (104) mixedwith hydrogen-rich gas (120) and hydrocarbon diluting agent (126) in theform of product recycle to the second catalytic zone (105) of ahydrotreating reactor (101) comprising a first catalytic zone (102)upstream of a second catalytic zone (105). The second hydrotreatedeffluent (106) is separated into a gaseous fraction (121) and a secondhydrotreated liquid (108) in separator (107). Gaseous fraction (121) maybe flashed again at a lower temperature into gaseous fraction (123),water rich fraction (125), and hydrocarbon rich fraction (124) inseparator (122). The first hydrotreated liquid (108) can be heated (109,111) and recompressed (110) and mixed with hydrogen-rich gas (120) toform the feed for the first catalytic zone (102) comprising, wherehydrodeoxygenation and hydrodenitrification is caused to obtain a firsthydrotreating effluent, from which a product side stream (112) can bewithdrawn. The product side stream (112) is stripped with hydrogen-richgas (120) in stripper (114) to form a stripped hydrotreated liquid(115), which is mixed with hydrogen-rich gas (120) and fed to anisomerisation reactor (103) comprising at least one catalytic zone,where the stripped hydrotreated liquid (115) is isomerised to obtain anisomerised effluent (116), which is separated into a gaseous fraction(118) and a isomerised liquid (119) in separator (117). The specificarrangement makes efficient use of fresh hydrogen for polishing in thefirst catalytic zone, providing a polished hydrocarbon product rich indissolved hydrogen, where part of such product (FIG. 1 , I (liquidoverflow)) and excess hydrogen gas (FIG. 1 , g) can be used ashydrocarbon diluent and make-up hydrogen in the downstreamhydrotreatment in the second catalytic zone, and/or withdrawn as aproduct side stream (112) between the polishing and hydrotreating bedand isomerised in an isomerisation reactor.

FIG. 2 is a comparative reactor setup referred to in comparative example1 and in table 7. It is similar to FIG. 1 , but omits the secondhydrotreating reactor. FIG. 2 describes feeding oxygenated hydrocarbonfeedstock (204) mixed with hydrogen-rich gas (220) and hydrocarbondiluting agent (226) to a first hydrotreatment reactor (201) comprisingat least one catalytic zone (205). The first hydrotreated effluent (206)is separated into a gaseous fraction (221) and a first hydrotreatedliquid (208) in separator (207). Gaseous fraction (221) may be flashedagain at a lower temperature into gaseous fraction (223), water richfraction (225), and hydrocarbon rich fraction (224) in separator (222).The first hydrotreated liquid (208) is stripped with hydrogen-rich gas(220) in stripper (214) to form a stripped hydrotreated liquid (215),which is mixed with hydrogen-rich gas (220) and fed to a firstisomerisation reactor (203) comprising at least one catalytic zone,where the stripped hydrotreated liquid (215) is isomerised to obtain afirst isomerised effluent (216), which is separated into a gaseousfraction (218) and a first isomerised liquid (219) in separator (217).

FIG. 3 is a comparative reactor setup referred to in comparative example2 and in table 7. It is similar to FIG. 1 , but does not include aseparation step between the first and second hydrotreating reactor. FIG.3 describes feeding oxygenated hydrocarbon feedstock (304) mixed withhydrogen-rich gas (320) and hydrocarbon diluting agent (326) in the formof product recycle to a first hydrotreatment reactor (301) comprising atleast one catalytic zone (305). The first hydrotreated effluent (306) ismixed with hydrogen-rich gas (320) to form the feed for the secondhydrotreating reactor (302) comprising at least one catalytic zone,where hydrodeoxygenation and hydrodenitrification is caused to obtain asecond hydrotreating effluent (330), which is separated into a gaseousfraction (321) and a second hydrotreating liquid (312) in separator(307). Gaseous fraction (321) may be flashed again at a lowertemperature into gaseous fraction (323), water rich fraction (325), andhydrocarbon rich fraction (324) in separator (322). The secondhydrotreating liquid (312) is stripped with hydrogen-rich gas (320) instripper (314) to form a stripped hydrotreated liquid (315), which ismixed with hydrogen-rich gas (320) and fed to a first isomerisationreactor (303) comprising at least one catalytic zone, where the strippedhydrotreated liquid (315) is isomerised to obtain a first isomerisedeffluent (316), which is separated into a gaseous fraction (318) and afirst isomerised liquid (319) in separator (317).

When describing the embodiments of the present invention, thecombinations and permutations of all possible embodiments have not beenexplicitly described. Nevertheless, the mere fact that certain measuresare recited in mutually different dependent claims or described indifferent embodiments does not indicate that a combination of thesemeasures cannot be used to advantage. The present invention envisagesall possible combinations and permutations of the described embodiments.

The terms “comprising”, “comprise” and comprises herein are intended bythe inventors to be optionally substitutable with the terms “consistingof”, “consist of” and “consists of”, respectively, in every instance.

EXAMPLES Example 1

Low quality waste material originating from rendered animal fat wastecontaining beef tallow, pork lard and chicken fat, was used as feedstockfor renewable fuel processing. The feedstock was purified usingpretreatment by bleaching before directing it to a hydrotreatmentprocess. Table 1 shows the carbon number distribution of the low-qualityanimal fat feedstock used before pretreatment measured by GC accordingto ISO 15304M.

TABLE 1 The carbon number distribution of the low-quality animal fatfeedstock before pretreatment analyzed by GC. Fatty acid distributionwt-% C14:0 2.32 C14:1 0.36 C15:0 0.17 C16:0 25.47 C16:1 2.29 C16:2 0.1C16:3 1.68 C17:0 0.48 C17:1 0 C18:0 23.55 C18:2 4.68 C18:3 0.59 C19:00.28 C19:1 0.14 C20:0 0.27 C20:1 0.57 C20:2 0.17 C20:3 0 C22:0 0.04unknown 1.9 TOTAL 100

TABLE 2 Properties of the feedstock before pretreatment Method PropertyAnimal fat waste EN ISO 12185 Density 15° C. 913.4 kg/m³ EN ISO 12185Density 50° C. 883.4 kg/m³ EN ISO 20846 Sulphur 71.5 ppm ASTMD4629/D5762 Nitrogen 1120 ppm ASTM D2710 Bromine index 24 g/100 g ISO3961 Iodine number 58 ASTM D3242 Free fatty acids (TAN) 1.00 mg KOH/gENISO12937 Water 0.05%

TABLE 3 Gel Permeation Chromatography (GPC) analysis on the feedstockcomponents before pretreatment. Component Amount (wt-%) Oligomers 0.4Triglycerides 75.3 Diglycerides 15.4 Monoglycerides 0.4 Carboxylic acids11.1

The feedstock was pretreated by bleaching before using it as feedstockfor the hydrotreatment processing whereby the amount of nitrogencalculated as total elemental nitrogen was decreased to 1000 w-ppm,which was thus the nitrogen impurity level of the feed stream whenentering it into hydrotreatment processing (see the entry “N content inthe feed to HDO” in table 4).

The feedstock to be processed by hydrotreatment contained nitrogenimpurities, inorganic and organic, the organic impurities being mainlyin the form of organic nitrogen compounds, such as amides and amines,which were analyzed from the feed. The amount of metal impurities, suchas Ca, Co, Fe, Mg, Mn, Ni and Zn, were less than 1 w-ppm which was theanalysis detection accuracy limit for the specific ICP determinationused. Equally, the amount of Al and Na impurities were less than 2w-ppm, and P content was less than 1 w-ppm.

To illustrate the invention with various amounts of nitrogen, thispretreated feedstock was mixed with palm oil having a nitrogen contentof 18 w-ppm to obtain six different concentrations of nitrogen (25, 75,150, 300, 500, 1000 w-ppm) used in run 1-6 of this example.

The pretreated feedstocks containing various amounts of nitrogen (freshfeed) were introduced as six separate runs into a hydrodeoxygenation(HDO) fixed bed trickle bed reactor set-up according to FIG. 1 . The HDOreaction was carried out in the presence of a catalyst bed (105)containing 45000 kg sulphided NiMo on alumina support (fresh catalysthaving a relative HDO activity compared to fresh HDO catalyst activity),under a pressure of 50 bar, a feed rate into the HDO reactor of 48000kg/h, a total feed rate WHSV of 1.1 h⁻¹ for catalyst bed (105), at a H₂flow of about 500 NI H₂/I feed, and at a reaction temperature of about309° C. measured at the HDO reactor inlet (T_(IN)), resulting in atemperature of about 340° C. at the HDO reactor outlet (T_(OUT)). Freshhydrogen feed into the reactor was 28700 m³/h (NTP) and the low-qualityanimal fat waste feed volume was 57 m³/h. Liquid HDO product wasrecycled as diluting agent (126), and the ratio of product recycle tothe fresh feed was about 6:1.

The effluent from the HDO reactor underwent separation into a liquid anda gaseous phase in a high temperature separator before being fed to thepolishing bed (102), located upstream of the HDO bed. The polishing bedis a fixed bed containing the same sulphided NiMo catalyst on aluminasupport as the HDO bed (fresh catalyst having a relative HDO activitycompared to fresh HDO catalyst activity), where the amount of thecatalyst material was 15000 kg. The polishing bed was operated under apressure of 50 bar, having a feed rate WHSV of about 8.2 h⁻¹ whencalculated based on the total liquid feed, and the polishing bed inlettemperature (T_(IN)) was about 340° C., i.e. 31° C. higher than the HDOinlet temperature. The hydrogen amount used was about 25 vol-% of theamount of hydrogen used in the HDO catalyst bed.

Table 4 shows the results of the test runs (run 1-6) with a set-up asshown in FIG. 1 , as described above, where a combined HDO reactor and apolishing bed is used, where the gaseous by-products including nitrogencontaining compounds are removed in between the two beds. As evidentfrom table 4, the nitrogen content after the polishing step can be keptlow despite very high nitrogen contents of the fresh feed. The lownitrogen amount is desirable in a product for various reasons, inparticular because low nitrogen amounts influences the isomerisationreaction thereby causing better cold flow properties under identicalisomerisation conditions compared to a product having a higher nitrogenamount prior to isomerisation (data not shown).

The nitrogen content may be decreased to ≤0.4 w-ppm by modifying theprocessing conditions, in particular increasing the processingtemperature of the polishing bed. The final nitrogen impurity was ≤0.3w-ppm in all the runs (1-6). Increasing the temperature in the HDO bedtypically leads to uncontrollable reactions causing poor cold propertiesin the final isomerised product. After the hydrodeoxygenation andpolishing the final liquid paraffinic effluent was hydroisomerized in anisomerization reactor. The isomerization was carried out in a fixed bedtrickle bed reactor in the presence of a Pt-SAPO-catalyst under apressure of 40 bar, with WHSV of 1.5 h⁻¹ and a reaction temperature of328° C. Hydrogen to feed ratio was 300 normal litres H₂ per litre feed.

The very low nitrogen content of all the experiments led to productswith excellent cold properties. After isomerization and separation bydistillation an aviation fuel cut was obtained having a T10 (° C.)cut-off temperature from 185 to 205, a T90 (° C.) cut-off temperaturefrom 270 to 295° C. and final boiling point (° C.) from 275 to 300° C.,fulfilling the ASTM D7566 (2016), Annex A2 specification, having adensity of less than 772 kg/m³ (measured according to ASTM 4052 (2018))and a freezing point of less than −40° C. (measured according to IP529).The obtained aviation fuel component further has a turbidity point lowerthan −30° C. (determined according to ASTM D5771 (2017)) with anexcellent yield of about 60 wt-%.

TABLE 4 HDO reactor and polishing bed - fresh catalyst - FIG. 1 Run 1Run 2 Run 3 Run 4 Run 5 Run 6 Unreacted feed vs paraffin content at wt %0.4 0.5 0.6 0.7 0.8 0.9 the entry into polishing bed (127) Unreactedfeed vs paraffin content at wt % <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 the entryinto the isomerization reactor (115) N content in the feed to HDO (104)w-ppm 25 75 150 300 500 1000 N content in the feed to HDO diluted w-ppm5 15 28 56 92 183 1:6 with HDO recycle N content in the liquid effluentfrom w-ppm 3 7 13 25 42 81 the HDO catalyst bed before entering thepolishing catalyst bed (108) N content before entering w-ppm <0.3 <0.3<0.3 <0.3 <0.3 <0.3 isomerization reactor (115) Bromine Index (115)mg/100 g <20 <20 <20 <20 <20 <20

Comparative example 1

A reactor set-up according to FIG. 2 was tested as an alternative forefficiently removing the undesired oxygen and nitrogen impurities. Inthe set-up of FIG. 2 , the same feed composition to example 1 wasapplied and essentially the same operating conditions (temperature,pressure, catalysts, etc.) were used as in example 1, with the exceptionthat in this reactor set-up there was no polishing bed (102) downstreamof the HDO reactor. Rather in this example the entire catalyst amount offresh catalyst (60000 kg) was in a single HDO reactor. The HDO reactionwas carried out under a pressure of 50 bar, a feed rate into the HDOreactor of 48000 kg/h, a total feed rate WHSV of 0.8 h⁻¹, at a H₂ flowof about 590 NI H₂/I feed, and at a reaction temperature of about 308°C. measured at the HDO reactor inlet (T_(IN)), resulting in atemperature of about 340° C. at the HDO reactor outlet (T_(OUT)). Freshhydrogen feed into the reactor was 33400 m³/h (NTP) and the low-qualityanimal fat waste feed volume was 57 m³/h. Liquid HDO product wasrecycled as diluting agent, and the ratio of product recycle to thefresh feed was about 6:1.

Table 5 shows the results from the runs in a single HDO reactor as shownin FIG. 2 , where the gaseous by-products including nitrogen containingcompounds are removed after the HDO reactor before entering the liquidparaffinic effluent into the isomerisation stage.

As can be seen from table 5, the nitrogen content before theisomerisation reactor of all runs (7-12) were higher compared to thenitrogen content in example 1. The same amount of catalyst was used incomparative example 1 compared to example 1, but now inside a singlereactor. This comparison shows that a single reactor is not able toremove the nitrogen in a similar efficient manner as in the case ofsplitting the catalyst volume into two separate reactors and removingthe gaseous phase between these two reactors.

The increased nitrogen content in feed inevitably led to an increase ofnitrogen in the final liquid paraffinic effluent stream to theisomerization thus resulting in poorer cold properties and yield for theaviation fuel component retrieved from the separation distillation afterisomerization. A turbidity point of about −10° C. was obtained withaviation fuel yield of 5 wt-% in the run 12 where the nitrogen initialcontent was 1000 ppm.

TABLE 5 Single HDO reactor only - fresh catalyst - FIG. 2 Run 7 Run 8Run 9 Run 10 Run 11 Run 12 Unreacted feed vs paraffin content wt % 0.10.1 0.1 0.1 0.2 0.3 at the entry into the isomerization reactor (215) Ncontent in the feed to HDO ppm 25 75 150 300 500 1000 (204) N content inthe feed to HDO w-ppm 5 14 28 55 90 180 diluted 1:6 with HDO recycle Ncontent in liquid effluent (208) ppm 2.5 6.8 13 25 42 83 N contentbefore Isomerisation ppm 0.6 0.9 1.1 1.5 2.0 2.9 reactor (215) BromineIndex (215) mg/100 g 87 113 134 159 183 219

Comparative Example 2

A reaction set-up as depicted by FIG. 3 , otherwise similar to example 1with the exceptions that two HDO reactors in series were used and thatthere was no gas removal after the first HDO reactor before entering thefeed (306) into the second HDO reactor (302) downstream of the first HDOreactor (301). A catalyst bed similar to the polishing bed of FIG. 1 wasinstalled inside the second HDO reactor (302). The liquid paraffiniceffluent (306) from the first HDO reactor was directed directly to thesecond HDO reactor i.e. without removal of the gaseous by-productsincluding nitrogen containing compounds after the first HDO reactorbefore entering the liquid paraffinic effluent into the second HDOreactor. The final liquid paraffinic effluent stream (312) obtainedafter the second HDO reactor (302) was directed to the stripper (314)for removal of the gaseous impurities, and subsequently into theisomerization reactor. The catalysts and reaction conditions were thesame as for example 1.

This reactor setup was similar to the prior art reactor setup describedin US 2011/0094149 A1.

As can be seen from table 6, the nitrogen content of all the runs(13-18) caused much higher nitrogen contents compared to the nitrogencontents in example 1.

The set-up according to FIG. 3 was found to be able to reduce the loweramounts of nitrogen impurities, at lower amounts of nitrogen content inthe initial feed, e.g. about 25 ppm of nitrogen or less. However, whenthe amount of nitrogen is increased to 150 wppm or higher in the freshfeed, the nitrogen remaining after the HDO and polishing was increasedto a value of 0.8 ppm, or higher. The increase of nitrogen content inthe isomerization resulted in poorer cold properties and yield for theaviation fuel component retrieved from the separation distillation afterisomerization, a turbidity point of about −15° C. was obtained withaviation fuel yield of 10 wt-% in the run 18 where the nitrogen initialcontent was 1000 ppm.

TABLE 6 two HDO reactors - fresh catalyst - FIG. 3 Run 13 Run 14 Run 15Run 16 Run 17 Run 18 Unreacted feed vs paraffin content % 0.3 0.4 0.50.6 0.7 0.8 at the entry into second HDO reactor (liquid phase)Unreacted feed vs paraffin content % 0.1 0.1 0.1 0.1 0.1 0.2 at theentry into the isomerization reactor (315) N content in the feed to HDO(304) w-ppm 25 75 150 300 500 1000 N content in the feed to HDO w-ppm 514 27 53 88 198 diluted 1:6 with HDO recycle N content before enteringw-ppm 4.4 13 25 50 83 166 polishing N content before entering w-ppm 0.40.6 0.8 1.2 1.6 2.3 isomerization reactor (315) Bromine Index (315) mg/79 103 120 143 165 198 100 g

23-46. (canceled)
 47. Process for preparing hydrocarbons from anoxygenated hydrocarbon feedstock having a nitrogen impurity of 10 wppmor more, measured as elemental nitrogen, comprising: a hydrotreatmentreactor comprising a first catalytic zone arranged above a secondcatalytic zone, in which a hydrotreatment entry stream comprising theoxygenated hydrocarbon feedstock, a hydrogen-rich gas, and optionally aproduct recycle diluting agent, is introduced to the second catalyticzone at an inlet between the first and the second catalytic zone, whereit is mixed with part of a first hydrotreated effluent from the firstcatalytic zone, wherein said part of said first hydrotreated effluentcomprises liquid hydrocarbons with dissolved hydrogen, where the secondcatalytic zone is operated at a temperature and a pressure causing atleast hydrodeoxygenation and hydrodenitrification to an extent where asecond hydrotreated effluent from the second catalytic zone of thehydrotreatment reactor contains mainly hydrocarbons, and wherein theoxygenated hydrocarbon feedstock has been converted to >95%hydrocarbons; the second hydrotreated effluent from the second catalyticzone of the hydrotreatment reactor is subjected to a separation stagewhere at least part of the second hydrotreated effluent is separatedinto a gaseous fraction and a hydrotreated liquid), where thehydrotreated liquid contains >95 wt % hydrocarbons and >1 wppm nitrogen;at least part of the hydrotreated liquid and a hydrogen-rich gas isintroduced in the hydrotreatment reactor (101) to the first catalyticzone, at an inlet temperature that is higher than the inlet temperaturein the second catalyst zone of the hydrotreatment reactor and at apressure causing hydrodeoxygenation and hydrodenitrification; a productside stream containing part of the first hydrotreated effluent from thefirst catalytic zone is taken out between the first and second catalyticzones, the product side stream containing a liquid component and agaseous component, and where the liquid component of the side streamcontains >99 wt % hydrocarbons and <1 wppm nitrogen, preferably <0.4wppm nitrogen, measured as elemental nitrogen; optionally isomerisingthe side stream in an isomerisation reactor comprising at least onecatalytic zone, in which the product side stream and a hydrogen-richgas, the hydrogen-rich gas containing <1 ppm (mol/mol) nitrogen,measured as elemental nitrogen, is introduced into the catalytic zone atan inlet temperature and a pressure causing at least hydroisomerisationto produce an isomerised effluent; the isomerised effluent from theisomerisation reactor is subjected to a separation stage, where theisomerised effluent is separated into a gaseous fraction and anisomerised liquid, where the isomerised liquid contains >30 wt %branched hydrocarbons, and/or an increase in branched hydrocarbonsof >30 wt % compared to the second hydrotreated liquid, wherein part ofthe first hydrotreated effluent from the first catalytic zone heats thehydrotreatment entry stream, and wherein the inlet temperature andpressure of the second catalyst zone is 200-400° C. and 10-150 bar, andwherein the inlet temperature and pressure of the first catalyst zone is250-450° C. and 10-150 bar.
 48. Process according to claim 47, where theside stream is subjected to a stripping stage, where the side stream isstripped with a stripping gas (H2) causing the stripped side stream tohave <0.4 wppm nitrogen, measured as elemental nitrogen, such as <0.3wppm nitrogen, and a lower nitrogen amount compared to the side stream;isomerising the stripped side stream in an isomerisation reactorcomprising at least one catalytic zone, in which the stripped sidestream and a hydrogen-rich gas having <1 ppm (mol/mol) nitrogen,measured as elemental nitrogen, is introduced into the catalytic zone ata temperature and a pressure causing at least hydroisomerisation toproduce a first isomerisation effluent; the isomerised effluent from thefirst isomerisation reactor is subjected to a separation stage, wherethe isomerised effluent is separated into a gaseous fraction and anisomerised liquid, where the first isomerised liquid contains >30 wt %branched hydrocarbons.
 49. Process according to claim, 47, wherein theisomerised liquid is separated into at least an aviation fuel having afreeze point of −40° C. or lower, such as −47° C. or lower.
 50. Processaccording to claim 47, wherein cooling is applied during the separationstage of the second hydrotreated effluent to an extent that the secondhydrotreated liquid has a temperature below the inlet temperature of thefirst catalytic zone of the first hydrotreatment reactor.
 51. Processaccording to claim 47, where a hydrocarbon diluting agent as well as afresh oxygenated hydrocarbon feedstock is not introduced to the firstcatalytic zone of the hydrotreatment reactor.
 52. Process according toclaim 47, where the extent of hydrodeoxygenation andhydrodenitrification in the second catalytic zone is controlled in sucha manner that in the first catalytic zone, the temperature increasebetween the inlet of the first catalytic zone and the outlet of thefirst catalytic zone is not more than 10° C.
 53. Process according toclaim 47, wherein the second catalytic zone in the hydrotreatmentreactor has a lower hydrodeoxygenation activity than the first catalyticzone in the hydrotreatment reactor.
 54. Process according to claim 47,wherein the hydrogen-rich gas used in the first catalyst zone contains<5 wppm nitrogen impurities, measured as elemental nitrogen.
 55. Processaccording to claim 47, wherein the inlet temperature and pressure of thesecond catalyst zone is 200-400° C. and 10-150 bar, such as 250-380° C.and 20-120 bar, such as 280-360° C. and 30-100 bar.
 56. Processaccording to claim 47, wherein the second catalytic zone of thehydrotreatment reactor comprise one or more catalyst(s) selected fromhydrogenation metal on a support, such as for example a catalystselected from a group consisting of Pd, Pt, Ni, Co, Mo, Ru, Rh, W or anycombination of these, preferably the second catalytic zone comprise oneor more catalyst(s) selected from CoMo, NiMo, NiW, CoNiMo on a support,for example an alumina support.
 57. Process according to claim 47,wherein the hydrotreatment reactor is operated at a WHSV in the rangefrom 0.5-3 h-1; and a H2 flow of 350-900 NI H2/I feed.
 58. Processaccording to claim 47, wherein the inlet temperature and pressure of thefirst catalyst zone (102) is 250-450° C. and 10-150 bar, such as300-430° C. and 20-120 bar, such as 330-410° C. and 30-100 bar. 59.Process according to claim 47, wherein the first catalytic zone of thehydrotreatment reactor comprise one or more catalyst(s) selected fromhydrogenation metal on a support, such as for example a catalystselected from a group consisting of Pd, Pt, Ni, Co, Mo, Ru, Rh, W or anycombination of these, preferably the first catalytic zone comprise oneor more catalyst(s) selected from CoMo, NiMo, NiW, CoNiMo on a support,for example an alumina support.
 60. Process according to claim 47,wherein the inlet temperature and pressure of the isomerisation reactoris 280-370° C. and 20-50 bar.
 61. Process according to claim 47, whereinthe catalytic zones of the isomerisation reactor comprise one or morecatalyst(s) comprising a Group VIII metal on a support, where thesupport is selected from silica, alumina, clays, titanium oxide, boronoxide, zirconia, which can be used alone or as a mixture, preferablysilica and/or alumina.
 62. Process according to claim 61, wherein theone or more catalyst(s) further comprise a molecular sieve, such as azeolite.
 63. Process according to claim 47, wherein the isomerisationreactor is operated at a WHSV in the range from 0.5-1 h-1; and a H2 flowof 300-500 NI H2/I feed.
 64. Process according to claim 47, wherein theisomerised liquid has an iso- to n-paraffin ratio above 1, such as from5 to 30 or from 15 to
 30. 65. Process according to claim 47, wherein theoxygenated hydrocarbon feedstock has a nitrogen impurity 300 wppm ormore, preferably 500 wppm or more, measured as elemental nitrogen. 66.Process according to claim 47, wherein the hydrotreatment entry streamhas a nitrogen impurity of 100 to 500 wppm.
 67. Process according toclaim 47, wherein the second hydrotreated effluent from the secondcatalytic zone has a nitrogen impurity of 100 to 500 wppm or more. 68.Process according to claim 47, where the product side stream containingpart of the first hydrotreated effluent from the first catalytic zonethat is taken out between the first and second catalytic zones, theproduct side stream containing a liquid component and a gaseouscomponent, and where the liquid component of the side streamcontains >99 wt % hydrocarbons and <0.3 wppm nitrogen, measured aselemental nitrogen.
 69. Process according to claim 47, wherein theoxygenated hydrocarbon feedstock may contain 40 wt % or more of fattyacids or fatty acid esters.
 70. Process according to claim 47, whereinthe oxygenated hydrocarbon feedstock may be selected from plant oils andanimal fats.